The solubility of fullerene C70 in monocarboxylic acids C n - 1H2n - 1COOH (n = 1-9) over the temperature range 20-80°C

Article abstract of DOI:10.1134/S0036024408060344

The isothermal (20°C) solubility of fullerene C₇₀ in solvents of the homologous series of monocarboxylic acids C _{n - 1}H_{2n - 1}COOH (n = 1-9) and polythermal solubility over the temperature range 20-80°C of fullerene C₇

Full text of DOI:10.1134/S0036024408060344

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2008, Vol. 82, No. 6, pp. 1045–1047. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © K.N. Semenov, N.A. Charykov, O.V. Arapov, V.A. Keskinov, A.K. Pyartman, M.S. Gutenev, O.V. Proskurina, M.Yu. Matuzenko, V.V. Klepikov, 2008,
published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 6, pp. 1183–1186.
SHORT
COMMUNICATIONS
The Solubility of Fullerene C70 in Monocarboxylic Acids
Cn – 1H2n – 1COOH (n = 1–9) over the Temperature Range 20–80ꢀC
K. N. Semenova, N. A. Charykovb, O. V. Arapovb, V. A. Keskinovb, A. K. Pyartmanb,
M. S. Gutenevb, O. V. Proskurinac, M. Yu. Matuzenkoc, and V. V. Klepikovc
a St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199164 Russia
b ZAO “Innovatsii Leningradskikh Institutov i Predpriyatii,” St. Petersburg, Russia
c St. Petersburg Technological Institute (Technical University), Moskovskii pr. 26, St. Petersburg, 198013 Russia
e-mail: semenov1986@yandex.ru
Received June 4, 2007
Abstract—The isothermal (20°C) solubility of fullerene C70 in solvents of the homologous series of monocar-
boxylic acids Cn – 1H2n – 1COOH (n = 1–9) and polythermal solubility over the temperature range 20–80°C of
fullerene C70 in solvents of the homologous series of monocarboxylic acids Cn – 1H2n – 1COOH (n = 4–9) were
studied. The corresponding solubility diagrams were obtained and characterized.
DOI: 10.1134/S0036024408060344
INTRODUCTION
used Ó-xylene of ch. d. a. (pure for analysis) grade
and monocarboxylic acids of the homologous series
This work continues a series of studies initiated by
us in [1, 2]. It is concerned with the solubility of pure
light fullerene ë70 in solvents of the homologous series
of saturated unbranched acids.
Data on the solubility of fullerenes are of primary
importance for the development of methods for the iso-
lation of fullerenes from fullerene soot or a mixture of
fullerenes by crystallization and extraction and chro-
matographic and prechromatographic separation of
ë
n – 1H2n – 1ëOOH (n = 1–9) of kh. ch. (chemically
pure) grade with terminal carboxyl groups.
Experimental studies of the isothermal and poly-
thermal solubility of pure fullerene ë70 in carboxylic
acids over the temperature range 20–80°ë were per-
formed by the isothermal saturation method in a tem-
perature-controlled shaker (see [2] for more details).
Concentrations after every stage of saturation with
fullerene mixture components. They are also necessary pure fullerene ë70 were determined spectrophotometri-
for studies of chemical reactions with the participation cally on a SPECORD M-32 spectrophotometer at the
of fullerenes [1–5].
wavelengths λ = 335.5 and 472.0 nm (see [2] for more
details).
Note that the literature data on the solubility of ë70
are few (solubility was only studied in 20 solvents; tak-
ing into account new work [2], in 30 solvents) likely
because of comparative inaccessibility of this fullerene.
The content of solvents in crystal solvates was deter-
mined as follows. A solid phase freshly precipitated
from the corresponding solution in carboxylic acid was
two times washed with ethanol, dried at 20°ë for
30 min, and weighed. The product was then repeatedly
washed in a Soxhlet apparatus with ethanol (at 78°ë
and 1 atm), dried in a vacuum (0.1 torr) at 200°ë for
1 h, and weighed once more. The content of the solvent
in the initial crystal solvate (or solid solution of
fullerenes on its base) was determined from the weight
loss.
The solubility of another light fullerene, ë60, and
industrial fullerene mixture (ë60 : ë70 : ën > 70 = 65 : 32 :
3 wt %) in monocarboxylic acids was studied in [6].
According to [6], the temperature dependence of the
solubility of pure fullerene ë60 and the components of
the substitution solid solution was nonmonotonic
because of the formation of ë60 · ën – 1H2n – 1COOH
monosolvates in the solid phase (in ë60–carboxylic acid
binary systems) and solid solution monosolvates
(ë60)x(ë70)1 – x · ën – 1H2n – 1COOH (in ë60–ë70–carboxy-
lic acid ternary systems).
RESULTS AND DISCUSSION
By way of example, the electronic absorption
spectra of pure fullerene ë70 in three carboxylic acids
are shown in Fig. 1. We see that the spectra are quite
EXPERIMENTAL
Studies were performed for fullerene ë70 of purity stable and fully correspond to the absorption spectra
99.5 wt % with the major determinable impurity ë60 of light fullerenes in one-component aromatic sol-
(~0.5 wt %) from ZAO ILIP (St. Petersburg). We vents (benzene, toluene, Ó-xylene, Ó-dichloroben-
1045

1046
D, arb. units
SEMENOV et al.
S, mg/l
λm1 ax = 335.7 nm
0.8
300
200
1
2
3
0.6
0.4
0.2
0
λm2 ax = 472.0 nm
100
0
1
3
5
7
9
n
300
400
500
600
700
λ, nm
Fig. 2. Isotherm of the solubility of ë in monocarboxylic
70
acid homologues ë
H
ëOOH (n = 1–9) at 20°ë; S is
n – 1 2n – 1
Fig. 1. Examples of the optical spectra of solutions of ë
70
the solubility (mg/l), and n is the number of carbon atoms in
ëOOH acids.
in monocarboxylic acids ë
H
ëOOH: (1) enanthic,
n – 1 2n – 1
ë
H
n – 1 2n – 1
(2) pelargonic, and (3) caprylic. The solutions were diluted
with o-xylene in a 1 : 25 ratio, solutions of the correspond-
ing acids in o-xylene (the same dilution) were used as refer-
ence solutions. D is the optical density (arb. units), and λ is
the wavelength (nm).
perature grows. All diagrams consist of two solubility
branches, one of which (the low-temperature branch)
corresponds to the crystallization of fullerene ë70 bisol-
vate, C70 · 2ën – 1H2n – 1ëOOH, and the other, to the crys-
tallization of unsolvated ë70. Each diagram contains
one nonvariant point (O in Fig. 3) of the so-called tran-
sition type [8, 9]. This point corresponds to saturation
with both solid phases simultaneously.
zene, etc. [7]). This justifies calculations of the con-
centration of ë70 with the use of the empirical for-
mula obtained in [2].
The isotherm of solubility of ë70 in solvents of the
homologous series of carboxylic acids ën – 1H2n – 1ëOOH
(n = 1–9) is shown in Fig. 2. Note a fairly unusual shape
of the isotherm (a similar isotherm was obtained for the
homologous series of n-alkanols-1 [2]). A solubility
maximum is well seen for the dependence of the con-
centration of ë70 in saturated solutions (mg/l) on the
number of carbon atoms in acids. The maximum corre-
sponds to the ë6H13ëOOH acid.
It is noteworthy that, generally, the shape of the
polythermal dependences shown in Fig. 3 is fairly char-
acteristic of ë70 and closely agrees with the literature
data available [10].
The inverse temperature dependences of the log-
arithm of the mole fraction of ë70 in saturated solu-
tions are shown in Fig. 4. It is noteworthy that these
dependences are almost linear, which is, in turn, evi-
dence of a constant activity coefficient of ë70 in sat-
urated binary solutions (the activity coefficient is
independent of temperature and the concentration of
The solubility polytherms obtained are shown in
Fig. 3, and the isothermal and polythermal data on the
solubility of ë70 are summarized in the table.
Note that the temperature dependences of the solu- fullerene itself). Note that ë60 was also shown to
bility of ë70 are fairly close to each other. We always have constant activity coefficients in solutions [2, 3,
observe a monotonic increase in solubility as the tem- 11].
Solubility of fullerene C70 (mg/l) in monocarboxylic acids Cn − 1H2n − 1COOH at various temperatures
Solvent
20°C
30°C
40°C
50°C*
60°C
70°C
80°C
Butyric
13.3
13.8
125
16.1
19.7
131
18.5
21.7
140
22.1
25.9
146
37.1
30.9
150
36.1
33.4
150
47.9
38.9
154
Valeric
Caproic
Enanthic
Caprylic
Pelargonic
330
357
380
381
401
447
439
110
135
152
153
154
154
166
56.2
56.9
58.1
57.1
84.0
101
117
Note: The solubility of C in formic, acetic, and propionic acids at 20°C is 0.1, 1.7, and 4.0 mg/l, respectively (was not determined at
70
other temperatures). The equilibrium solid phase is unsolvated C at temperatures above 50°C and C · 2C
H
COOH bisol-
70
70
n − 1 2n − 1
vates below 50°C.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 82 No. 6 2008

THE SOLUBILITY OF FULLERENE C70
1047
–lnXC(1)
S, mg/l
(‡)
O
70
O
120
C70 · 2C8H17COOH
C70 · 2C4H9COOH
1
2
3
6
10
80
40
0
5
4
11
3
C70 · 2C3H7COOH
12
13
C70 · 2C6H13COOH
2
(b)
O
1
2.8 2.9 3.0 3.1 3.2 3.3
3.4
C70 · 2C5H11COOH
103/T, K–1
400
4
5
6
Fig. 4. Dependences of the logarithm of the mole fraction of
in saturated solutions on inverse temperature in the
ë
70
series of monocarboxylic acids ë
H
ëOOH (n = 4–9):
300
200
n – 1 2n – 1
C70 · 2C7H15COOH
(1) butyric, (2) valeric, (3) pelargonic, (4) caproic,
(5) caprylic, and (6) enanthic.
cal peculiarity of polythermal solubility diagrams (frag-
ments of meltability diagrams) of particular systems.
100
20
30
40
50
t, °C
60
70
80
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Fig. 3. Polytherms of the solubility of ë in monocarbox-
70
ylic acids ë
H
ëOOH (n = 4–9); (a) n = (1) 4, (2) 5,
n – 1 2n – 1
and (3) 9 and (b) n = (4) 6, (5) 7, and (6) 8.
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certainly, the formation of such solvates is noticeably
more typical of the other fullerene, ë60. In [2], we did
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ë70–n-alkanol-1 binary systems (ë1–ë11) even at 20°C.
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formed over the whole homologous series studied (ë4–
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(see Figs. 3, 4). This constancy, which cannot be
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RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 82 No. 6 2008